CONSTITUENTS OF SOILS. 403 



1009. COMPOSITION OF SOILS. Many of 



Of what are J 



soils com- the above substances are contained in the 

 pose ' soil in extremely small proportion. Soils 



are principally composed of vegetable matter in a state 

 of decay, with clay, sand, and carbonate of lime. The 

 vegetable matter consists of the remains of plants of 

 previous years, and the clay, lime, and sand, are the 

 product of the gradual crumbling and decomposition 

 of rocky crust of the earth. 



1010. USE OF VEGETABLE MATTER IN 



State the uses 



of vegetable SOILS. The wood, leaves, and twigs of 

 oih T m which vegetable matter is composed, fur- 

 nish, in their gradual decay, the potash, 

 silica, and other constituents of their own skeletons to 

 form the framework of new plants. The organic mat- 

 ter is, at the same time, converted into ammonia and 

 carbonic acid ; these constitute the gaseous food on 

 which all vegetable life is sustained. 



1011. ADDITION OF VEGETABLE AND ANI- 

 K$Zd -AL MATTER._The addition of more of 

 by the addi- this material to the soil, in the form of peat 



tion of vegeta- - / 



bh and animal or muck from swamps, is of great advan- 



ta S e ? because it increases the supply of the 

 two important classes of materials which 

 have been mentioned. Animal matter of all kinds, 

 whether decomposed, as in stable manure and guano, 

 or in its original condition in the form of flesh, wool, 

 and bones, is a still more valuable addition to the soil. 

 The reason of its higher value, consists in the fact 

 that while it yields most of the other substances which 

 decaying vegetable matter supplies, it furnishes ammo- 



